Insulin resistance – a condition where the body’s cells fail to respond normally to the glucose control hormone insulin – increases the risk of developing type 2diabetes and pre diabetes. Now, a team shows that removing or blocking a protein mainly secreted by immune cells reverses diabetic insulin resistance and glucose intolerance in obese and diabetic mice.

The team – including researchers from the University of California-San Diego (UCSD) – reports what it discovered about the protein galectin-3 or Gal3 in the journal Cell.

Senior author Jerrold Olefsky, a professor of medicine at UCSD School of Medicine, remarks:

“This study puts Gal3 on the map for insulin resistance and diabetes in mouse model.”

Most people with diabetes have type 2diabetes, largely due to excess body weight and physical inactivity. Until recently, type 2diabetes was only seen in adults, but now more and more children are developing it.

If diabetes goes untreated, there is a high chance of hyperglycaemia, or raised blood sugar, which over time causes serious damage to vital parts of the body, including nerves and blood vessels.

In 2014, global estimates suggest 8.5 per cent of adults were living with diabetes – up from 4.7 per cent in 1980. In 2012, an estimated 1.5 million people died as a direct result of diabetes, and another 2.2 million as a result of high blood glucose.

Rates of diabetes have been rising more rapidly in middle- and low-income countries. In the United States, rates of new cases of diagnosed diabetes have started to fall, but the numbers are still very high.

Over 29 million Americans are thought to have diabetes, and 86 million have pre diabetes – a serious condition that raises the risk of developing type 2diabetes and other chronic diseases.

In the new study, he and his colleagues explain how immune cells called macrophages – which destroy targeted cells – play an important role in inflammation.

In obese humans and mice, macrophages and other immune cells accumulate in fat tissue. The researchers note that around 40 per cent of cells in fat tissue in obese subjects are macrophages.

The secretion of Gal3 attracts more macrophages, setting up a vicious cycle that result in ever-increasing levels of the signalling protein and accumulation of the immune cells.

In lab experiments, the researchers found that Gal3 was produced by bone marrow-derived macrophages and that secretion of the protein leads to insulin resistance in liver, muscle, and fat cells – even when there is no inflammation.

They also found giving mice Gal3 leads to insulin resistance and glucose intolerance, while blocking it in obese mice – either with drugs or by silencing a gene – improves insulin sensitivity.

“Importantly,” note the authors, “we found that Gal3 can bind directly to the insulin receptor (IR) and inhibit downstream IR signalling.”

Other studies have already linked Gal3 to other diseases. The team now plans to find out if the signalling protein could be a target for the treatment of conditions such as non-alcoholic fatty liver disease and heart and liver fibrosis.

Our findings suggest that Gal3 inhibition in people could be an effective anti-diabetic approach.” said Prof. Jerrold Olefsky